A major food reserve hidden under Antarctic sea ice has been discovered by a robot submarine.

The expedition in the Southern Ocean found that stocks of krill under the ice were five times more concentrated than those in open waters.

The shrimp-like species is a key food for penguins, whales and fish.

The importance of sea ice as a nursery for krill has long been suspected.
However, these findings are the first large-scale measurements of the breeding ground's existence.

Krill distribution

The discovery was made by UK scientists from the British Antarctic Survey, the Open University and the Marine Laboratory, Aberdeen.

Dr Brierley with the Autosub

The operation was the first under-ice mission for the £5m Autosub, one of the most advanced underwater probes ever made.

Project leader Dr Andrew Brierley, based at the University of St Andrews, said: "Discovery of this band is a major new insight because it shows that it is the ice edge, rather than sea ice generally, that is important for krill.

"Large reductions in ice area, perhaps following melting due to regional climatic warming, might not be so harmful to krill populations because, in summer at least, krill are not widely distributed under ice."

Natural surroundings

The krill, which graze the underside of sea ice, were detected by a special echo sounder.

"Prior to the advent of Autosub, it was impossible to investigate the environment under sea ice over ranges of more than a few metres," said Dr Brierley.

Krill is a key food for several species

"Scuba divers have looked under ice but they can only spend limited periods of time underwater and can only see short distances.

"Ice breaking ships can penetrate the pack ice to make biological measurements but, while breaking the ice, they can disturb any natural krill/ice associations."

Climate change

The unmanned submarine, which runs on torch batteries, was designed, built and operated by Southampton Oceanography Centre.

The team also says that it has made the first ever continuous measurements of Antarctic sea ice thickness, which can show the effect of climate change.

The submarine will now spend three years exploring beneath ice shelves up to a kilometre thick to investigate their role in the Earth's climate.